1. Field of the Invention
The present invention relates to a substrate carrying device that floats a substrate by the agency of a gas, such as air, and carries the floating substrate, a substrate carrying method, and a computer-readable storage medium storing programs for accomplishing the substrate carrying method.
2. Description of the Related Art
A carrying arm is most prevalently used as a substrate carrying mechanism in a semiconductor device fabricating process. The carrying arm needs a mechanism for advancing and retracting the carrying arm and a mechanism for moving the carrying arm along a carrying passage. Those mechanisms for a carrying arm for carrying a large substrate are inevitably large. Driving units for driving those mechanisms are considerably large when the carrying arm carries, for example, a 12 in. diameter or 16 in. diameter wafer. When such large driving units are used, a dust removing measure, such as creation of special exhaust flow, needs to be taken to suppress the adhesion of particles produced by the abrasion of the driving units to the substrate. A large semiconductor device fabricating system is needed to process a large substrate. Therefore, the semiconductor device fabricating system needs to be built in the simplest possible construction.
In view of those necessary conditions, a substrate carrying mechanism that carries a substrate by a carrying method that floats a substrate by the agency of a gas and carries the floating substrate is advantageous because a carrying device provided with such a substrate carrying mechanism can be built in a thin structure. A known substrate carrying mechanism mentioned in, for example, Patent document 1 carries a substrate by such a carrying method. This known substrate carrying mechanism will be briefly described with reference to FIGS. 19(a) and 19(b) respectively showing this known substrate carrying mechanism in a top view and a longitudinal sectional view. Shown in FIGS. 19(a) and 19(b) are a flat structure 11 forming a carrying passage, and a top plate 12 included in the flat structure 11. Many gas spouting pores 13 are arranged at intervals all over the top plate 12. The gas spouting pores 13 extend obliquely through the top plate 12. As shown in FIG. 19(c), the gas spouting pores 13 are formed such that the gas is spouted obliquely upward in a direction from one end, namely, a first end on the left-hand side in FIG. 19(c), toward the other end, namely, a second end on the right-hand side in FIG. 19(c), of the carrying passage through the gas spouting pores 13. A bottom member is attached to the top plate 12 to define a closed space 15. A gas supply pipe 16 has one end connected to the flat structure 11 and the other end connected to a gas source to supply, a compressed gas, such as compressed air, into the closed space 15.
Compressed air is supplied through the gas supply pipe 16 into the closed space 15 after the wafer W, namely, a substrate, has been placed on a part of the carrying passage on the side of the first end in this substrate carrying mechanism. The air is spouted through the gas spouting pores 13 obliquely upward as shown in FIG. 19(c). The air pushes up the wafer W from the top plate 12 to float the wafer W. The air flows along the lower surface of the wafer W toward the second end of the carrying passage to propel the floating wafer W toward the second end of the carrying passage. Thus the wafer W is carried from the first end to the second end of the carrying passage.
Since any frictional force acts on the floating wafer W, the wafer W is unstable and is moved by a slight force. Thus the substrate is liable to be caused to drift longitudinally or transversely by a slight force. Therefore, the gas spouting pores 13 need to be precisely formed to prevent the wafer W from drifting away from a correct position. However, it is difficult, in general, to form many pores obliquely to the thickness of such a plate and hence it is possible that the air flow for carrying the wafer W is disturbed to cause troubles in carrying the wafer W and the substrate carrying mechanism needs a high manufacturing cost.
Air of a high cleanliness must be used for carrying the wafer W so that the air may not affect a process for processing the carried wafer W adversely. Air consumption rate increases with the length of the carrying passage and hence the running cost of the substrate carrying mechanism is high when the carrying passage is long.
Although methods that use air for carrying a substrate are widely known, practical application of those methods is difficult because of those foregoing problems.
For example, a coating and developing system for coating a substrate with a resist film and processing the substrate by a developing process has many processing units. Those processing units are stacked in layers in processing blocks. Efforts are made to carry a substrate directly from one to the other of the processing unit of the block. Although a flotation carrying mechanism is thin and is advantageous in carrying a substrate for a long distance. The foregoing problems hinder the practical application of the flotation carrying mechanism.    Patent document 1: JP-A 57-128940, p. 2, 11, 12 to 17, lower left-hand col.